Tailored carbon dioxide capacity in carboxylate-based ionic liquids.

We have used a library of thermally stable tetraalkylphosphonium carboxylate ionic liquids that were easily prepared from available carboxylic acids. Depending on the pKa in water of the precursor acids, the resulting ionic liquids either dissolve or reversibly chemically absorb CO2, with some exhibiting notable gas capacities, reaching a CO2 mole fraction of 0.2 at 1 bar and 343 K. While equilibrium constants and ionic liquid capacities generally correlate with the pKa of the acids, certain exceptions underscore the influence of liquid structure and physical properties of the ionic liquids, elucidated through molecular dynamics simulations and density functional theory calculations. Unlike the trends observed in other CO2-absorbing ILs, phosphonium carboxylates do not experience increased viscosity upon gas absorption; instead, enhanced diffusivities are observed, facilitating efficient gas-liquid transfer.

Deep eutectic solvents on a tightrope: balancing the entropy and enthalpy of mixing.

The large melting point depressions characterising deep eutectic solvents (DESs) are related to negative deviations from ideal mixing behaviour characterised by the excess Gibbs energy. Favourable excess Gibbs energies result from a balance between the excess entropy and enthalpy of mixing, which was experimentally determined for three choline chloride (ChCl) based mixtures using calorimetry. While the excess Gibbs energy of H2O + ChCl is enthalpy dominated, those of ethylene glycol (EG) + ChCl and 1,3-propanediol + ChCl are entropy dominated. Molecular dynamics simulations using polarisable force-fields show intermolecular hydrogen bonds between DES constituents for H2O + ChCl and EG + ChCl. Hence, inter-species hydrogen bonding does not guarantee enthalpy-dominated melting point depressions. We suggest future research to focus on tuning the entropy-enthalpy balance via the chemical nature of the DES constituents.

Physical properties and nanostructuring of long-chained homobaric imidazolium ionic liquids.

Understanding the structure-property relationship and nanoscopic behaviour of ionic liquids is of utmost importance for their potential applications. Focusing these studies on sets of homobaric ionic liquids could provide important insight into the effects of specific chemical groups on the overall interaction profile, bringing researchers one step closer to succesfully designing ionic liquids which are tailor-made for specific applications. This work focuses on ionic liquids with 12 total carbons on their side chains, studying both their bulk physical properties (such as densities and viscosities) and their nanostructuring. The results reveal that by keeping the total number of carbons constant, but arranging them differently around the imidazolium ring, either in a linear or in a branched-chain formation, can result in compounds with quite distinct properties. Some of those (such as diffusivity) appear to be more sensitive to symmetry variations, while others (such as density) are not significantly affected. X-ray scattering is used in order to get a clearer understanding of the nanostructuring of the studied compounds and to investigate to what extent the observed macroscopic properties are directly linked to the nanoscale ordering.

Effect of ion structure on the physicochemical properties and gas absorption of surface active ionic liquids.

Surface active ionic liquids (SAILs) combine useful characteristics of both ionic liquids (ILs) and surfactants, hence are promising candidates for a wide range of applications. However, the effect of SAIL ionic structures on their physicochemical properties remains unclear, which limits their uptake. To address this knowledge gap, in this work we investigated the density, viscosity, surface tension, and corresponding critical micelle concentration in water, as well as gas absorption of SAILs with a variety of cation and anion structures. SAILs containing anions with linear alkyl chains have smaller molar volumes than those with branched alkyl chains, because linear alkyl chains are interdigitated to a greater extent, leading to more compact packing. This interdigitation also results in SAILs being about two orders of magnitude more viscous than comparable conventional ILs. SAILs at the liquid-air interface orient alkyl chains towards the air, leading to low surface tensions closer to n-alkanes than conventional ILs. Critical temperatures of about 900 K could be estimated for all SAILs from their surface tensions. When dissolved in water, SAILs adsorb at the liquid-air interface and lower the surface tension, like conventional surfactants in water, after which micelles form. Molecular simulations show that the micelles are spherical and that lower critical micelle concentrations correspond to the formation of aggregates with a larger number of ion pairs. CO2 and N2 absorption capacities are examined and we conclude that ionic liquids with larger non-polar domains absorb larger quantities of both gases.

A membrane-depolarizing toxin substrate of the Staphylococcus aureus type VII secretion system mediates intraspecies competition.

The type VII protein secretion system (T7SS) is conserved across Staphylococcus aureus strains and plays important roles in virulence and interbacterial competition. To date, only one T7SS substrate protein, encoded in a subset of S. aureus genomes, has been functionally characterized. Here, using an unbiased proteomic approach, we identify TspA as a further T7SS substrate. TspA is encoded distantly from the T7SS gene cluster and is found across all S. aureus strains as well as in Listeria and Enterococci. Heterologous expression of TspA from S. aureus strain RN6390 indicates its C-terminal domain is toxic when targeted to the Escherichia coli periplasm and that it depolarizes the cytoplasmic membrane. The membrane-depolarizing activity is alleviated by coproduction of the membrane-bound TsaI immunity protein, which is encoded adjacent to tspA on the S. aureus chromosome. Using a zebrafish hindbrain ventricle infection model, we demonstrate that the T7SS of strain RN6390 promotes bacterial replication in vivo, and deletion of tspA leads to increased bacterial clearance. The toxin domain of TspA is highly polymorphic and S. aureus strains encode multiple tsaI homologs at the tspA locus, suggestive of additional roles in intraspecies competition. In agreement, we demonstrate TspA-dependent growth inhibition of RN6390 by strain COL in the zebrafish infection model that is alleviated by the presence of TsaI homologs.

The Unexplored Wealth of Microbial Secondary Metabolites: the Sphingobacteriaceae Case Study.

Research on secondary metabolites (SMs) has been mostly focused on Gram-positive bacteria, especially Actinobacteria. The association of genomics with robust bioinformatics tools revealed the neglected potential of Gram-negative bacteria as promising sources of new SMs. The family Sphingobacteriaceae belongs to the phylum Bacteroidetes having representatives in practically all environments including humans, rhizosphere, soils, wastewaters, among others. Some genera of this family have demonstrated great potential as plant growth promoters, bioremediators and producers of some value-added compounds such as carotenoids and antimicrobials. However, to date, Sphingobacteriaceae's SMs are still poorly characterized, and likewise, little is known about their chemistry. This study revealed that Sphingobacteriaceae pangenome encodes a total of 446 biosynthetic gene clusters (BGCs), which are distributed across 85 strains, highlighting the great potential of this bacterial family to produce SMs. Pedobacter, Mucilaginibacter and Sphingobacterium were the genera with the highest number of BGCs, especially those encoding the biosynthesis of ribosomally synthesized and post-translationally modified peptides (RiPPs), terpenes, polyketides and nonribosomal peptides (NRPs). In Mucilaginibacter and Sphingobacterium genera, M. lappiensis ATCC BAA-1855, Mucilaginibacter sp. OK098 (both with 11 BGCs) and Sphingobacterium sp. 21 (6 BGCs) are the strains with the highest number of BGCs. Most of the BGCs found in these two genera did not have significant hits with the MIBiG database. These results strongly suggest that the bioactivities and environmental functions of these compounds, especially RiPPs, PKs and NRPs, are still unknown. Among RiPPs, two genera encoded the production of class I and class III lanthipeptides. The last are associated with LanKC proteins bearing uncommon lyase domains, whose dehydration mechanism deserves further investigation. This study translated genomics into functional information that unveils the enormous potential of environmental Gram-negative bacteria to produce metabolites with unknown chemistries, bioactivities and, more importantly, unknown ecological roles.

Design of Ionic Liquids for Fluorinated Gas Absorption: COSMO-RS Selection and Solubility Experiments.

In recent years, the fight against climate change and the mitigation of the impact of fluorinated gases (F-gases) on the atmosphere is a global concern. Development of technologies that help to efficiently separate and recycle hydrofluorocarbons (HFCs) at the end of the refrigeration and air conditioning equipment life is a priority. The technological development is important to stimulate the F-gas capture, specifically difluoromethane (R-32) and 1,1,1,2-tetrafluoroethane (R-134a), due to their high global warming potential. In this work, the COSMO-RS method is used to analyze the solute-solvent interactions and to determine Henry's constants of R-32 and R-134a in more than 600 ionic liquids. The three most performant ionic liquids were selected on the basis of COSMO-RS calculations, and F-gas absorption equilibrium isotherms were measured using gravimetric and volumetric methods. Experimental results are in good agreement with COSMO-RS predictions, with the ionic liquid tributyl(ethyl)phosphonium diethyl phosphate, [P2444][C2C2PO4], being the salt presenting the highest absorption capacities in molar and mass units compared to salts previously tested. The other two ionic liquids selected, trihexyltetradecylphosphonium glycinate, [P66614][C2NO2], and trihexyl(tetradecyl)phosphonium 2-cyano-pyrrole, [P66614][CNPyr], may be competitive as far as their absorption capacities are concerned. Future works will be guided on evaluating the performance of these ionic liquids at an industrial scale by means of process simulations, in order to elucidate the role in process efficiency of other relevant absorbent properties such as viscosity, molar weight, or specific heat.

Systematic Comparison of the Structural and Dynamic Properties of Commonly Used Water Models for Molecular Dynamics Simulations.

Water is a unique solvent that is ubiquitous in biology and present in a variety of solutions, mixtures, and materials settings. It therefore forms the basis for all molecular dynamics simulations of biological phenomena, as well as for many chemical, industrial, and materials investigations. Over the years, many water models have been developed, and it remains a challenge to find a single water model that accurately reproduces all experimental properties of water simultaneously. Here, we report a comprehensive comparison of structural and dynamic properties of 30 commonly used 3-point, 4-point, 5-point, and polarizable water models simulated using consistent settings and analysis methods. For the properties of density, coordination number, surface tension, dielectric constant, self-diffusion coefficient, and solvation free energy of methane, models published within the past two decades consistently show better agreement with experimental values compared to models published earlier, albeit with some notable exceptions. However, no single model reproduced all experimental values exactly, highlighting the need to carefully choose a water model for a particular study, depending on the phenomena of interest. Finally, machine learning algorithms quantified the relationship between the water model force field parameters and the resulting bulk properties, providing insight into the parameter-property relationship and illustrating the challenges of developing a water model that can accurately reproduce all properties of water simultaneously.

Improved carbon dioxide absorption in double-charged ionic liquids.

Four divalent ionic liquids based on imidazolium cations with alkyl or ether functionalized side-chains were synthesised and characterized: 3,3'-(tetraethyleneglycol-1,11-diyl)bis(1-methyl-1H-imidazolium)bromide, [tetraEG(mim)2][Br]2, 3,3'-(tetraethyleneglycol-1,11-diyl)bis(1-methyl-1H-imidazolium)acetate, [tetraEG(mim)2][OAc]2, 1-butyl-3-methylimidazolium malonate, [C4mim]2[Mal], and 3-butyl-1-methylimidazolium glutarate, [C4mim]2[Glut]. Their densities vary between 1.1 and 1.5 g cm-3 and their viscosities between 0.2 and 4 Pa s at 353 K. We found that the molar volumes are not additive, especially in the case of the divalent ionic liquids based on the double-charged imidazolium cations, meaning that they cannot be predicted using common group contribution methods. The reason for this behaviour could be explained by the structure of the cations, which is dominated by intramolecular hydrogen bonding. The carboxylate-based divalent ionic liquids absorb reversibly large quantities of carbon dioxide following a chemical mechanism described before. An improved 1 : 1 stoichiometry is achieved both in a double-charged imidazolium acetate ionic liquid and in imidazolium carboxylate salts with double charged anions. This behaviour places these ionic liquids amongst the best performing for carbon dioxide absorption.

Mixing divalent ionic liquids: effects of charge and side-chains.

We have prepared novel divalent ionic liquids (ILs) based on the bis(trifluoromethylsulfonyl)imide anion where two charged imidazolium groups in the cations are either directly bound to each other or linked by a single atom. We assessed the influence of the side-chain functionality and divalency on their physical properties and on the thermodynamics of mixing. The results indicate that shortening the spacer of a divalent IL reduces its thermal stability and increases its viscosity. Mixtures of divalent and monovalent ILs show small but significant deviations from ideality upon mixing. These deviations appear to depend primarily on the (mis)match of the nature and length of the cation side-chain. The non-ideality imposed by mixing ILs with different side-chains appears to be enhanced by the increase in formal charge of the cations in the mixture.

Connecting chloride solvation with hydration in deep eutectic systems.

The Deep Eutectic Solvents/Systems (DESs) choline chloride:urea (xChCl = 0.33) and choline chloride:glycolic acid (xChCl = 0.5) were investigated using viscosity-corrected 35Cl NMR spectroscopy and molecular dynamics simulations to probe the role of chloride as a function of water content. Three Cl- solvation regimes are revealed, with high-symmetry environments for pure and highly dilute DES, and an unusual low-symmetry interstitial region where the primary coordination sphere is most disordered.

Liquids with permanent porosity.

Porous solids such as zeolites and metal-organic frameworks are useful in molecular separation and in catalysis, but their solid nature can impose limitations. For example, liquid solvents, rather than porous solids, are the most mature technology for post-combustion capture of carbon dioxide because liquid circulation systems are more easily retrofitted to existing plants. Solid porous adsorbents offer major benefits, such as lower energy penalties in adsorption-desorption cycles, but they are difficult to implement in conventional flow processes. Materials that combine the properties of fluidity and permanent porosity could therefore offer technological advantages, but permanent porosity is not associated with conventional liquids. Here we report free-flowing liquids whose bulk properties are determined by their permanent porosity. To achieve this, we designed cage molecules that provide a well-defined pore space and that are highly soluble in solvents whose molecules are too large to enter the pores. The concentration of unoccupied cages can thus be around 500 times greater than in other molecular solutions that contain cavities, resulting in a marked change in bulk properties, such as an eightfold increase in the solubility of methane gas. Our results provide the basis for development of a new class of functional porous materials for chemical processes, and we present a one-step, multigram scale-up route for highly soluble 'scrambled' porous cages prepared from a mixture of commercially available reagents. The unifying design principle for these materials is the avoidance of functional groups that can penetrate into the molecular cage cavities.

Tuning the solvation of indigo in aqueous deep eutectics.

The solubility of synthetic indigo dye was measured at room temperature in three deep eutectic solvents (DESs)-1:3 choline chloride:1,4-butanediol, 1:3 tetrabutylammonium bromide:1,4-butanediol, and 1:2 choline chloride:p-cresol-to test the hypothesis that the structure of DESs can be systematically altered, to induce specific DES-solute interactions, and, thus, tune solubility. DESs were designed starting from the well-known cholinium chloride salt mixed with the partially amphiphilic 1,4-butanediol hydrogen bond donor (HBD), and then, the effect of increasing salt hydrophobicity (tetrabutylammonium bromide) and HBD hydrophobicity (p-cresol) was explored. Measurements were made between 2.5 and 25 wt. % H2O, as a reasonable range representing atmospherically absorbed water, and molecular dynamics simulations were used for structural analysis. The choline chloride:1,4-butanediol DES had the lowest indigo solubility, with only the hydrophobic character of the alcohol alkyl spacers. Solubility was highest for indigo in the tetrabutylammonium bromide:1,4-butanediol DES with 2.5 wt. % H2O due to interactions of indigo with the hydrophobic cation, but further addition of water caused this to reduce in line with the added water mole fraction, as water solvated the cation and reduced the extent of the hydrophobic region. The ChCl:p-cresol DES did not have the highest solubility at 2.5 wt. % H2O, but did at 25 wt. % H2O. Radial distribution functions, coordination numbers, and spatial distribution functions demonstrate that this is due to strong indigo-HBD interactions, which allow this system to resist the higher mole fraction of water molecules and retain its solubility. The DES is, therefore, a host to local-composition effects in solvation, where its hydrophobic moieties concentrate around the hydrophobic solute, illustrating the versatility of DES as solvents.

Participation and Performance in the Oldest Ultramarathon-Comrades Marathon 1921-2019.

Participation and performance trends have been analyzed for different ultramarathons for limited time periods. This study examined trends in participation and performance in the oldest ultramarathon in the world, the 'Comrades Marathon' (South Africa), during a century (1921-2019). Data from www.ultra-marathon.org on 100 000 unique finishers were analysed using different general linear models. Women represented 4.2% of the total sample (n=4152), and the first women ran this race in 1978. Before the year 1965, the number of participants in the race ranged between 5 and 35 athletes, then started to grow exponentially until mid 90's. An increase in finishers in the 70 s mainly due to an increase in male athletes in age groups 30-39, 40-49 and 50-59 years was observed (p<0.001). A stable running speed for overall women and men but an improvement in performance for the annual top five women and men were shown (p<0.001). Male runners were faster than female runners for all age groups (p<0.001). While overall performance was not improved across years, the annual top five women and men were able to improve their performance over years.

A methodology to empower citizens towards a low-carbon economy. The potential of schools and sustainability indicators.

Environmental empowering to control resource consumption and environmental impacts is critical to engage citizens to adopt more sustainable habits. This study demonstrates the potential benefits of innovative approaches based on sustainability indicators towards a low-carbon economy. A methodology to measure and promote sustainability in schools has been proposed and evaluated, aiming at showing the environmental performance and informing of potential environmental savings. The methodology, titled ClimACT, has two main purposes: measuring the environmental performance of schools through a school sustainability index based on measurable indicators in the areas of transport, procurement, green spaces, indoor air quality, energy, water and waste; and encouraging students, teachers and families towards an energy-efficient and low-carbon pathway through a structural procedure based on roles, activities and progress evaluation. The approach, applied to 39 pilot schools from Portugal, Spain, France and Gibraltar, achieved promising and encouraging results. All schools deployed the methodology successfully, achieving measurable environmental benefits in 95% of cases, with an average improvement of 10% in the global performance of schools after one year. Moreover, the 5112 surveys applied to school communities, before and after the methodology implementation, highlighted how the sustainable indicators had a significant influence on the daily lives of families, leading to improvements of their behaviour, with an average increase of 20% in indicators regarding good practices in transport, energy, water, waste and citizenship. The environmental empowering through measurable indicators is a step forward a low-carbon economy. This methodology is open and adaptable to all sectors and requirements.

High-Performance Porous Ionic Liquids for Low-Pressure CO2 Capture*.

Porous ionic liquids are non-volatile, versatile materials that associate porosity and fluidity. New porous ionic liquids, based on the ZIF-8 metal-organic framework and on phosphonium acetate or levulinate salts, were prepared and show an increased capacity to absorb carbon dioxide at low pressures. Porous suspensions based on phosphonium levulinate ionic liquid absorb reversibly 103 % more carbon dioxide per mass than pure ZIF-8 at 1 bar and 303 K. We show how the rational combination of MOFs with ionic liquids can greatly enhance low pressure CO2 absorption, paving the way towards a new generation of high-performance, readily available liquid materials for effective low pressure carbon capture.

Self-assembled nanostructures in ionic liquids facilitate charge storage at electrified interfaces.

Driven by the potential applications of ionic liquids (ILs) in many emerging electrochemical technologies, recent research efforts have been directed at understanding the complex ion ordering in these systems, to uncover novel energy storage mechanisms at IL-electrode interfaces. Here, we discover that surface-active ILs (SAILs), which contain amphiphilic structures inducing self-assembly, exhibit enhanced charge storage performance at electrified surfaces. Unlike conventional non-amphiphilic ILs, for which ion distribution is dominated by Coulombic interactions, SAILs exhibit significant and competing van der Waals interactions owing to the non-polar surfactant tails, leading to unusual interfacial ion distributions. We reveal that, at an intermediate degree of electrode polarization, SAILs display optimum performance, because the low-charge-density alkyl tails are effectively excluded from the electrode surfaces, whereas the formation of non-polar domains along the surface suppresses undesired overscreening effects. This work represents a crucial step towards understanding the unique interfacial behaviour and electrochemical properties of amphiphilic liquid systems showing long-range ordering, and offers insights into the design principles for high-energy-density electrolytes based on spontaneous self-assembly behaviour.

The afc antifungal activity cluster, which is under tight regulatory control of ShvR, is essential for transition from intracellular persistence of Burkholderia cenocepacia to acute pro-inflammatory infection.

The opportunistic pathogen Burkholderia cenocepacia is particularly life-threatening for cystic fibrosis (CF) patients. Chronic lung infections with these bacteria can rapidly develop into fatal pulmonary necrosis and septicaemia. We have recently shown that macrophages are a critical site for replication of B. cenocepacia K56-2 and the induction of fatal pro-inflammatory responses using a zebrafish infection model. Here, we show that ShvR, a LysR-type transcriptional regulator that is important for biofilm formation, rough colony morphotype and inflammation in a rat lung infection model, is also required for the induction of fatal pro-inflammatory responses in zebrafish larvae. ShvR was not essential, however, for bacterial survival and replication in macrophages. Temporal, rhamnose-induced restoration of shvR expression in the shvR mutant during intramacrophage stages unequivocally demonstrated a key role for ShvR in transition from intracellular persistence to acute fatal pro-inflammatory disease. ShvR has been previously shown to tightly control the expression of the adjacent afc gene cluster, which specifies the synthesis of a lipopeptide with antifungal activity. Mutation of afcE, encoding an acyl-CoA dehydrogenase, has been shown to give similar phenotypes as the shvR mutant. We found that, like shvR, afcE is also critical for the switch from intracellular persistence to fatal infection in zebrafish. The closely related B. cenocepacia H111 has been shown to be less virulent than K56-2 in several infection models, including Galleria mellonella and rats. Interestingly, constitutive expression of shvR in H111 increased virulence in zebrafish larvae to almost K56-2 levels in a manner that absolutely required afc. These data confirm a critical role for afc in acute virulence caused by B. cenocepacia that depends on strain-specific regulatory control by ShvR. We propose that ShvR and AFC are important virulence factors of the more virulent Bcc species, either through pro-inflammatory effects of the lipopeptide AFC, or through AFC-dependent membrane properties.

Probing the Reorganization of Ionic Liquids' Structure Induced by CO2 Sorption.

The sorption of CO2 is often used to modify the macroscopic properties of liquids and solids. In the particular case of ionic liquids, different from molecular liquids, the sorption of CO2 may not induce volume expansions due to the strong Coulombic interactions between the ions of the fluid. However, a considerable viscosity decrease has been systematically observed. In order to understand the mechanisms of properties modifications in ionic fluids, herein we used Raman spectroscopy to probe the effect of CO2 on the structure of ionic liquids. It is shown that CO2 perturbs the electrostatic interactions between cations and anions, thus inducing a change in the polar domain of ionic liquids. It is observed that ionic liquids having bulkier ions are more prone to be perturbed by CO2 in comparison to ionic liquids having smaller ions. These results reveal new means of controlling the electrostatic forces between the ions and contributes to the mechanistic understanding of the modification of the macroscopic properties of ionic liquids by CO2 sorption.